Wood can be modified and improved in properties like hardness, stiffness, strength, dimensional stability and resistance to deterioration by impregnating it with various compounds.
Currently, wood is made more durable mainly by using preservatives such as CCA. Most of these preservatives have toxicity to organisms in the environment, including humans. Even if they are well-fixed in wood, their presence presents a problem for disposal at the end-of-life. WO 2005/018889 for instance discloses a method for protecting wood against fungal degradation. The method consists of impregnating the wood with a fluid treatment agent such as for instance liquid wood smoke or wood smoke vapour containing biologically active compounds, such as for instance furan compounds. After impregnation, the impregnated wood is allowed to dry. The active compounds are not reacted in the wood. A disadvantage of such approach is that the utilized furan compounds have biocidal effects not only towards fungi but also towards other organisms in the environment.
Several approaches were designed to use more environmentally-friendly chemicals such as: i) use of water-soluble salts which have low toxicity ii) use of heat treatment such as the Plato process and iii) use of non-toxic chemicals which react with and alter the wood cell walls, making them less susceptible to deterioration (e.g. acetylation, N-methylolation, furfurylation).
Approach i) has the drawback that such salts usually leach out of wood in contact with water, limiting their usefulness. This approach is also less effective than traditional creosote and CCA treatment because of the low toxicity of these compounds, in addition higher concentrations are needed to obtain acceptable results.
Approach ii) has the drawback that such a treatment gives insufficient protection to the wood and the treated wood has poor mechanical properties.
An example of approach iii) is based on the impregnation of wood with monomeric furfuryl alcohol. Previous art used undiluted treating solution, and treated the wood to high levels of retention. The main disadvantage with this treatment is the large amount of chemical used and the resulting cost.
Furfuryl alcohol is highly water soluble and therefore easily forms a uniform solution with water which can be used to impregnate wood. However, there are several requirements needed before a useful modified wood can be made. First, after being impregnated into wood, the solution must be polymerized and reacted with wood at elevated temperatures (curing temperature) to be useful. Second, the polymerization must occur in wet or dry wood.
Chemical initiators were therefore added to the furfuryl alcohol to make it polymerize after impregnation at elevated temperatures (80-120° C.) in wet or dry wood. An example of a prior art initiator is zinc chloride. However zinc chloride has a devastating effect on cellulose degradation and thereby on the long-term strength properties of the modified wood.
New catalytic systems for furfurylation in wood were developed using for example cyclic carboxylic anhydrides. WO 02/30638 describes how to initiate furfuryl alcohol and make it polymerize and react with wood at the curing temperature. However, the initiated furfuryl alcohol from that technology does not mix well with water. Combining furfuryl alcohol and initiators causes the mixtures to separate into two components which cannot be uniformly impregnated into wood.
EP 1 341 648 describes a furan polymer impregnated wood obtained by impregnating wood with a mixture containing furfuryl alcohol monomers and one further compound. Furfuryl alcohol treated wood however suffers from loss of reactant and emission of unreacted monomers.
Woods treated with furfuryl alcohol can have problems to meet current requirements for health and safety, because of VOC emission due to unreacted components. Increasing awareness about environment and health and safety for human beings calls for extra attention in the preparation of modified wood. Increasing strictness of environmental rules demands a decrease of the emission of harmful substances. Modified wood with low VOC emissions are therefore required.
An alternative for the use of traditionally preserved woods involve tropical hardwoods. However, such woods are very expensive and supply and quality thereof are not consistent. Also, governments, NGO's and media are paying close attention to the use of products made of tropical wood in the context of environmental issues such as deforestation, scracers sources, illegal logging, etc. . . . There is therefore a need in the art for alternatives to tropical hardwoods.
In view of the above, it is clear that there remains a need in the art for an improved method for modifying wood. It is therefore a main object of the present invention to provide a modified wood having improved properties and an improved method for preparing such modified wood.
More in particular, the invention aims to provide modified wood showing lower VOC emission and a method for preparing such modified wood. The present invention further aims to provide modified wood showing improved properties as regards to durability, fire resistance, shrink efficiency, dimensional stability, surface hardness, UV stability, cracking resistance, rot resistance, decay resistance, and the like. Yet another object is to provide modified wood, which is uniform in color and density throughout the treated zone, and a method for preparation thereof.
It is further another object of the invention to provide modified wood and a method for preparation thereof, showing enhanced resistance to degradation by biological organisms such as e.g. wood decay fungi, but without showing toxic or biocidal effects towards such biological organisms.
Another object of the invention is to provide an improved composition adapted for impregnating wood and use thereof for impregnating and modifying wood. The invention further aims to provide a composition for impregnating and modifying wood having improved storage stability, such that during storing no phase separation occurs.
According to the present invention, the foregoing and other objects are attained by a product, method and uses thereof as disclosed in the patent claims.